class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        int n=nums.size();
        sort(nums.begin(),nums.end());
         vector<vector<int>>ret;
        for(int i=0;i<n;)
        {
            for(int j=i+1;j<n;)
            {
                long long aim=(long long)target-(nums[i]+nums[j]);
                int left=j+1;int right=n-1;
                while(left<right)
                {
                    int sum=nums[left]+nums[right];
                    if(sum>aim)right--;
                    else if(sum<aim)left++;
                    else
                    {
                        ret.push_back({nums[i],nums[j],nums[left++],nums[right--]});
                        while(left<right&&nums[left]==nums[left-1])left++;
                        while(left<right&&nums[right]==nums[right+1])right--;
                    }
                }
                j++;
                while(j<n&&nums[j]==nums[j-1])j++;
            }
            i++;
            while(i<n&&nums[i]==nums[i-1])i++;
        }
        return ret;
    }
};
